This application claims the benefit of Provisional Application Serial No. 60/315,605 filed Aug. 29, 2001.
1. Field of the Art
The present invention relates generally to a wind tunnel and to a collector design therefor, and more particularly to an open jet wind tunnel with a collector design to reduce resonance.
2. Description of the Prior Art
An existing and well-recognized problem with open jet wind tunnels is the pulsing or resonance which occurs at various frequencies. Open jet wind tunnels are used extensively in the automotive industry and various other industries for the purpose of determining aerodynamic forces on a test vehicle or other object. A typical configuration of an open jet wind tunnel includes a test section often comprising a large room or other closed configuration, a nozzle at the upstream end of the test section and a collector at the downstream end of the test section. Generated air flow flows along a flow path from the nozzle, across the test section and into the collector. During a test, the vehicle or other object to be tested is positioned in the test section within the air flow.
An observed problem with open jet wind tunnels which often restricts their use at certain air speeds includes a pulsing phenomenon or resonance which occurs at such air speeds. This pulsing or resonance, in some cases, may simply make the air flow and the floor pressures unsteady so as to adversely affect the air flow past the test object. In other cases, the pulsing or resonance may be strong enough to damage the building structure. Various authorities have recognized this problem in open jet wind tunnels and have speculated that such pulsing phenomenon or resonance is directly related to test section air speeds and wind tunnel dimensions and that the mechanism that excites such resonance involves the interaction of vortices of air flow from the nozzle to the collector. It has also been speculated that decreasing the length of the test section at a given air speed will have the tendency to reduce resonances at that sir speed However, this is a limitation on the capability of the system and is often not an option because of the test section length needed for a particular application. Accordingly, to the extent that this problem has been addressed, it has been primarily addressed by adjusting air speeds and/or wind tunnel and test section dimensions in an attempt to avoid the undesirable resonance problems. The result, however, is that this merely changes the frequency or air speed conditions at which the resonance or the pulsing phenomenon occurs or places other significant limitations upon the system.
Accordingly, there is a need in the art for a wind tunnel construction, and in particular an open jet wind tunnel, which not only minimizes, but preferably eliminates, resonance problems for desired air speed and the wind tunnel dimensions.
In contrast to the prior art, the present invention is directed to an open jet wind tunnel design, and more particularly to a collector design for use in such wind tunnel, which minimizes, if not eliminates, resonance problems such as those described above for particular applications.
Specifically, the present invention focuses on the belief that the resonance is created at various frequencies as a result of eddies or other air flow between the exit edge of the nozzle exit and the leading edge of the collector. In conventional collector design, these edges are all uniformly spaced from one another. Thus, they combine their energies to excite the undesirable resonance. Although speculation exists that creating paths of unequal length between the nozzle and the collector will reduce high amplitude resonances, this has never been tested. In accordance with the present invention, the collector is designed and configured so that the spacing between the exit nozzle and the leading edge of the collector varies (or is non-uniform) from point to point along the collector edge. Thus, there is insufficient energy at any one frequency to excite an undesirable resonance.
In accordance with a preferred embodiment of the present invention, one or more sections of the leading edge of the collector are sloped relative to the exit nozzle and relative to a vertical plane orthogonal to the flow path of the air. Thus, air flowing from the exit nozzle toward the collector strikes the leading edge of the collector at different times because of the non-uniform spacing and therefore limits or suppresses the generation of undesirable resonance. In a most preferred embodiment of the invention, the leading edge of the collector includes a top edge section which is uniformly spaced from the exit nozzle, and a pair of sloping side edge sections which slope downwardly and away from the top section and thus results in a leading edge in which the distance from such edge to the exit nozzle or the above mentioned plane is non-uniform.
Accordingly, it is an object of the present invention to provide an improved open jet wind tunnel.
Another object of the present invention is to provide an open jet wind tunnel with a configuration which, minimizes, if not eliminates, undesirable resonance.
A further object of the present invention is to provide an open jet wind tunnel with an improved collector design which minimizes, if not eliminates, undesirable resonance.
A still further object of the present invention is to provide a collector design for an open jet wind tunnel in which points along the leading edge of the collector are non-uniformly spaced from the nozzle.
These and other objects of the present invention will become apparent with reference to the drawings, the description of the preferred embodiment and the appended claims.